In the prior art, as a high density optical recording medium, there have been known two methods, namely the method in which a metal, a semi-metal or an organic compound is melted or evaporated by a highly converged recording light such as a laser beam to form a concave portion or a pit portion, and the method in which discrimination pits are formed by a transfer between two thermodynamically semi-stable states such as crystalline and non-crystalline states.
These optical recording methods provide optical recording materials and tracking patterns for following an optical beam on generally rigid glass discs or plastic discs, and the medium recorded according to this method has been generally known as a medium shaped in optical recording disc. Such medium shaped in optical recording disc, while having the advantages of high dimensional precision and high mechanical strength, has on the other hand problems that the driving device becomes greater in scale, and also the medium as well as the device are expensive for the reasons such that the weight and the thickness become greater. Accordingly, such medium has not yet been generally prevailed widely. For an optical recording medium capable of high density recording to be generally prevailed widely, in addition to the medium shaped in optical recording disc of the prior art, advent of an optical recording medium which is lightweight, compact and yet inexpensive such as a medium shaped in optical record flexible disc, a medium shaped in optical recording card, a medium shaped in optical recording tape, a medium shaped in optical recording sheet has been awaited.
Of the two high density optical recording methods as described above, the first method must form a concave portion or a pit portion during recording. For this purpose, the substance must be taken away by melting or evaporation, whereby the mass transfer during recording becomes unavoidably great. Therefore, for making the recording sensitivity sufficiently large, it has been frequently practiced to make substance transfer readily occur by having the recording portion of the optical recording material exposed to the air. However, in this case, the optical recording material may be oxidized by the influence of the moisture in the air to cause deterioration, or foreign matter may be collided against the optical recording material, whereby there is a danger that an accident may occur such that the optical recording material may be mechanically destroyed. For this reason, there is employed a structure in which the optical recording material is sealed with a gap interposed therebetween. However, in a medium structure having such vacant space, both weight and thickness are increased, whereby it is difficult to give a diversity of shapes such as flexible disc, card, tape, sheet, etc.
On the other hand, the second method, namely the method in which transfer between the thermodynamically semi-stable states is utilized, due to small substance transfer during recording, the optical recording material is not required to be exposed to the air, but sealing is possible without provision of a gap. Therefore, according to the recording method by such transfer, it can correspond to a diversity of shapes of medium. In the prior art, as the material to be used for such transfer, crystalline--non-crystalline phase transfer materials such as TeO.sub.x, As-Te-Ge have been known. However, the phase transfer materials of the prior art tend to be remarkably unstabilized with lapse of time, and also the optical characteristic change amount between crystal and non-crystal is smaller as compared with the above pit portion formation, whereby it is not necessarily satisfactory with respect to precision of recording and reproduction.